Variable intake valve assembly for internal combustion engine

ABSTRACT

An intake valve assembly of an internal combustion engine that includes a combustion chamber and an intake passage. The intake valve assembly comprises an intake valve movable into and out of engagement with a valve seat, a reciprocating primary valve tappet, and a secondary valve tappet axially non-movably attached to the primary valve tappet. The intake valve is mounted to the primary valve tappet and axially freely movable relative thereto. The primary valve tappet is configured for axially engaging the first intake valve to limit the axial movement thereof said intake valve away from the valve seat. The secondary valve tappet is configured for axially engaging the intake valve for mechanically moving the intake valve away from the valve seat. The intake valve is further operated fluidly in response to pressure differential between the intake passage and the combustion chamber.

CROSS-REFERENCE TO RELATED APPLICATION

This Application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Application No. 61/041,382 filed Apr. 1, 2008 by Ralph Moore.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to internal combustion engines in general and, more particularly, to an intake valve assembly of an internal combustion engine.

2. Description of the Prior Art

In a conventional internal combustion engine, intake and exhaust poppet valves regulate the gas exchange. A valve train (i.e. cams, drive gears and chains, rocker arms, push rods, lifters, etc.) regulate the poppet valves. Fixed valve timing of the poppet valves of the conventional internal combustion engine, and especially of the intake valve, represents a compromise between two conflicting design objectives: 1) maximum effective pressure within a cylinder, thus torque, at the most desirable points in a range of engine operating speeds, and 2) a highest possible power peak output. The higher the RPM at which maximum power occurs, and the wider the range of an engine operating speed, the less satisfactory will be the ultimate compromise. Large variations in the effective flow opening of the intake valve relative to the stroke (i.e., in design featuring more than two valves) will intensify this tendency.

In conventional four-stroke internal combustion engines, during an ending phase of an exhaust stroke, both intake and exhaust valves are kept open simultaneously for a certain period (known in the art as a valve overlap period, or simply a valve overlap) in order to increase efficiency of a gas exchange process. However, efficient valve timing at valve overlap (especially intake valve opening) is sensitive to the engine speed. Too early intake valve opening at low engine speeds will allow a portion of the exhaust gas to be blown past the open intake valve. This is referred to as dilution and will reduce the power of the engine. Too late intake valve opening at high engine speeds prevents good exhaust gas scavenging and cylinder charging. This will also reduce the power of the engine. At the end of an induction stroke, the intake valve needs to be closed so that the rising piston can compress the new air/fuel charge. During this period, the valve timing efficiency is also dependent on the engine speed. If the intake valve is closed too late at slow engine speeds some of the new charge is pushed back into an intake passage. If the intake valve is closed too early at high engine speeds, the intake passage is sealed before it was finished filling the cylinder. It becomes obvious that in order to keep the engine operating at top efficiency, the valve timing has to be adjusted with engine speed changes.

Typically, a range of engine operating speeds includes a low engine speed range (low engine speeds) and a high engine speed range (high engine speeds). Generally, the low engine speed range is defined as a speed range from an idle speed to a midrange speed, and high engine speed is defined as a speed range from the midrange speed to a maximum engine speed. In other words, the low engine speed is the engine speed at or near the lower end of the operating speed range of the engine, while the high engine speed is the engine speed at or near the upper end of the operating speed range of the engine.

At the same time, growing demand for minimizing exhaust emissions and maximizing fuel economy means that a low idle speed and high low-end torque along with high specific output of an internal combustion engine are becoming increasingly important. These imperatives have led to the application of variable valve timing systems (especially for intake valves). However, this approach is complex and expensive, and takes away from durability of the internal combustion engine.

Thus, the intake valve assembly of the prior art, including but not limited to those discussed above, are susceptible to improvements that may enhance engine performance. The need therefore exists for an intake valve assembly that is simple in design, compact in construction and cost effective in manufacturing, and, at the same time, provides both an improved low-end torque along with a high power output of the internal combustion engine.

SUMMARY OF THE INVENTION

The present invention provides an intake valve assembly for an internal combustion engine that includes a combustion chamber and an intake passage fluidly communicating with the combustion chamber through an intake port.

The intake valve assembly of the present invention comprises an intake valve movable into and out of engagement with a valve seat formed in the intake port between respective closed and open positions, a primary valve tappet reciprocating between an innermost position and an outermost position, and a secondary valve tappet axially non-movably attached to said primary valve tappet. The intake valve has first and second contact surfaces axially spaces from each other, and seals the combustion chamber from the intake passage in the closed position thereof. In turn, the primary valve tappet has a primary tappet surface complementary to the first contact surface of the intake valve, while the secondary valve tappet has a secondary tappet surface complementary to the second contact surface of the intake valve.

The secondary tappet surface of the secondary valve tappet is axially spaced from the second contact surface of the intake valve when the primary tappet surface of the primary valve tappet is in engagement with the first contact surface of the intake valve. Moreover, the intake valve is coaxially mounted to the primary valve tappet and axially freely movable relative thereto between the primary tappet surface of the primary valve tappet and the secondary tappet surface of the secondary valve tappet.

The primary tappet surface of the primary valve tappet is configured for operatively axially engaging the first contact surface of the intake valve to limit the axial movement of the intake valve away from said valve seat and to place the intake valve in the closed position thereof when the primary valve tappet being in the innermost position thereof, while the secondary tappet surface of the secondary valve tappet is configured for operatively axially engaging the second contact surface of the intake valve for mechanically moving the intake valve away from the valve seat. Furthermore, the intake valve is operated both mechanically by both the primary and secondary valve tappets and fluidly in response to pressure differential between the intake passage and the combustion chamber.

Therefore, the present invention provides a novel intake valve assembly of an internal combustion engine that provides in effect a variable valve timing and significantly improves both low and high speed performance of the engine. Moreover, the present invention reduces cost and complexity of the valve assembly and valve train compared to the existing (conventional) variable valve timing systems, and requires minimal low cost modification to adapt the intake valve assembly of the present invention to existing engines.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the present invention will become apparent from a study of the following specification when viewed in light of the accompanying drawings, wherein:

FIG. 1 is a fragmentary, sectional transverse view of an internal combustion engine comprising an intake valve assembly according to the present invention;

FIG. 2 is a sectional view of the intake valve assembly according to a preferred embodiment of the present invention with an intake valve in a closed position and a primary valve tappet in an innermost position;

FIG. 3 is a sectional view of the intake valve assembly according to the preferred embodiment of the present invention with the intake valve in an open position and the primary valve tappet in an outermost position;

FIG. 4 is a cross-sectional view of the primary valve tappet of the intake valve assembly according to the preferred embodiment of the present invention;

FIG. 5 is a cross-sectional view of a secondary valve tappet of the intake valve assembly according to the preferred embodiment of the present invention;

FIG. 6 is a cross-sectional view of the intake valve according to the preferred embodiment of the present invention;

FIG. 7 is a partial cross-sectional view of the intake valve assembly according to the preferred embodiment of the present invention showing the intake valve and the secondary valve tappet mounted to the primary valve tappet;

FIG. 8 is a graph of cam and valve lift versus cam angle of an intake cam lobe and the primary valve tappet according to the preferred embodiment of the present invention;

FIG. 9 is a fragmentary, sectional transverse view of the internal combustion engine according to the preferred embodiment of the present invention during a beginning phase of an induction stroke at low engine speed;

FIG. 10 is a fragmentary, sectional transverse view of the internal combustion engine according to the preferred embodiment of the present invention during an ending phase of the induction stroke at low engine speed;

FIG. 11 is a fragmentary, sectional transverse view of the internal combustion engine according to the preferred embodiment of the present invention during the beginning phase of an induction stroke at high engine speed;

FIG. 12 is a fragmentary, sectional transverse view of the internal combustion engine according to the preferred embodiment of the present invention during the ending phase of the induction stroke at high engine speed;

FIG. 13 shows dynamometer test results for the conventional, stock engine; and

FIG. 14 shows dynamometer test results for the engine equipped with the intake valve assembly of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will now be described with the reference to accompanying drawing.

For purposes of the following description, certain terminology is used in the following description for convenience only and is not limiting. The words such as “upper” and “lower”, “left” and “right”, “inwardly” and “outwardly” designate directions in the drawings to which reference is made. The words “smaller” and “larger” refer to relative size of elements of the apparatus of the present invention and designated portions thereof. The terminology includes the words specifically mentioned above, derivatives thereof and words of similar import. Additionally, the word “a”, as used in the claims, means “at least one”.

Referring to FIG. 1 of the drawings, a preferred embodiment of an internal combustion engine of the present invention, generally denoted by reference numeral 10, is illustrated.

The engine 10 comprises a cylinder block 11 defining at least one hollow cylinder 12, a cylinder head 14 fastened to the cylinder block 11 to seal the upper end of the cylinder 12, and a piston 16 reciprocatingly mounted in the cylinder 12 and, in turn, conventionally connected to a crankshaft through a connecting rod (not shown). The cylinder 12 of the cylinder block 11, the cylinder head 14 and the piston 16 define a combustion chamber 15. The cylinder head 14 is provided with an intake (or induction) passage 18 fluidly communicating with the combustion chamber 15 through an intake port 20, and an exhaust passage 22 fluidly communicating with the combustion chamber 15 through an exhaust port 23. As further illustrated in detail in FIGS. 2 and 3, the intake port is defined by a substantially annular valve seat member 24 secured to the cylinder head 14. The valve seat member 24 has a substantially annular intake valve seat 25 (best shown in FIG. 3). Moreover, as used herein, the term “gas” or “fluid” will refer to an air or air/fuel mixture flowing through the intake passage 18 into the combustion chamber 15 through the intake port 20.

The engine 10 further comprises an intake valve assembly 30, an exhaust valve assembly 32, and a valve train (or valve actuating mechanism) 34 provided for actuating the intake and exhaust valve assemblies 30 and 32. The valve train 34, illustrated in FIG. 1, includes a first (intake) rocker arm 36 a actuating the intake valve assembly 30, a second (exhaust) rocker arm 36 b actuating the exhaust valve assembly 32, and a valve actuating cam 38. In turn, the cam 38 has a first (intake) lobe 38 a actuating the first rocker arm 36 a and a second (exhaust) lobe 38 b actuating the second rocker arm 36 b. The intake cam lobe 38 a has a fixed cam profile including a leading (opening) flank 38′ and a trailing (closing) flank 38″. Rotation of the crankshaft (not shown) causes the piston 16 to reciprocate in the cylinder 11 and the valve actuating mechanism 34 to operate in conventional manner to perform the known four-stroke engine operating cycle comprising intake, compression, expansion and exhaust strokes.

As illustrated in detail in FIGS. 2-6, the intake valve assembly 30 according to the present invention comprises an intake valve 42, a primary valve tappet 44 and a secondary valve tappet 46. Both the intake valve 42 and the secondary valve tappet 46 are mounted about the primary valve tappet 44 substantially coaxially therewith. Moreover, the secondary tappet 46 is non-movable fastened to the primary tappet 44.

The intake valve 42 is movable into and out of engagement with the valve seat 25 formed in the intake port 20 between respective closed and open positions so that in the closed position of the intake valve 42, the combustion chamber 15 is sealed from the intake passage 18. As illustrated in FIGS. 1-3, the combustion chamber 15 fluidly communicates with the intake passage 18 only when the intake valve 42 is in the open position.

As illustrated in detail in FIG. 4, the primary valve tappet 44 includes an elongated stem 48 and a disk-shaped tappet head 50 provided at a lower (or distal) end of the stem 48 of the primary valve tappet 44 for engaging the intake valve 42. The primary valve tappet 44 of the intake valve assembly 30 is operated by the intake lobe 38 a of the cam 38 actuating the first rocker arm 36 a of the valve train (or valve actuating mechanism) 34 of the engine 10. The valve actuating mechanism 34 operatively actuates the primary valve tappet 44 for reciprocating between an innermost position (shown in FIGS. 1 and 2) and an outermost position thereof (shown in FIG. 3) relative to the seat member 24 of the cylinder head 14.

The primary valve tappet 44 is biased toward the innermost position thereof by a valve spring 68 which engages an upper end of the stem 48 of the primary valve tappet 44. Preferably, the primary valve spring 50 is in the form of a coils spring mounted concentric to the stem 48 of the primary valve tappet 44.

As illustrated in detail in FIG. 5, the secondary valve tappet 46 is axially non-movably mounted about the stem 48 of the primary valve tappet 44 substantially coaxially therewith. The secondary valve tappet 46 comprises an elongated, tubular stem 54 mounted about the stem 48 of the primary valve tappet 44 substantially coaxially therewith. The tubular stem 54 of the secondary valve tappet 46 defines a cylindrical bore 55 therethrough and is provided with a valve spring retainer 56 formed at a distal end of the tubular stem 54 integrally therewith for holding (or retaining) the valve spring 68 in normally contracted condition. As further shown in FIGS. 1-3 and 7, the secondary valve tappet 46 is axially spaced from the intake valve 42 to a distance k (shown in FIG. 7) when the intake valve 42 is in engagement with the tappet head 50 of the primary valve tappet 44. As further illustrated in detail in FIGS. 2, 3 and 7, the valve spring retainer 56, thus the secondary valve tappet 46, is axially non-movably attached to the stem 48 of the primary valve tappet 44 using a conventional valve keeper 57. Consequently, the valve spring 68, being normally contracted, biases the primary valve tappet 44 in the innermost position thereof by its expansion force.

According to the preferred embodiment of the present invention, as illustrated in detail in FIG. 6, the intake valve 42 is a poppet valve including a hollow stem portion 60, and a disk-shaped valve head 62 provided at a lower end of the stem portion 60 for sealingly engaging the valve seat 25 of the valve seat member 24. The valve head 62 is complementary to the valve seat 25 of the valve seat member 25. Accordingly, when the valve head 62 of the poppet valve 42 engages the valve seat 25 of the valve seat member 24 in the closed position thereof (shown in FIGS. 1 and 2), the intake port 20 is blocked and the combustion chamber 15 is hermetically scaled from the intake passage 18. Moreover, the intake valve 42 defines a substantially cylindrical bore 61 extending through both the stem portion 60 and the valve head 62 of the intake poppet valve 42. Consequently, the stem 48 of the primary valve tappet 44 is axially extending through the cylindrical bore 61 in the intake valve 42 substantially coaxially therewith so that the hollow stem portion 60 of the poppet valve 42 is reciprocatingly and coaxially mounted to and about the stem 48 of the primary valve tappet 44. Preferably, the disk-shaped tappet head 50 of the primary valve tappet 44 is conical or dome-shaped and shaped so as to complement and nest in a cavity 65 formed in the valve head 62 of the intake valve 42, as illustrated in detail in FIG. 2.

Moreover, the disk-shaped valve head 62 of the intake valve 42 defines a first contact surface 64 provided on an axially bottom end of the valve head 62 of the intake valve 42 facing the tappet head 50 of the primary valve tappet 44, and a second contact surface 63 provided on an axially top end of the stem portion 60 of the intake valve 42 facing the secondary valve tappet 46.

The intake valve assembly 30 further includes a valve guide 70 supporting both the elongated tubular stem 54 of the secondary valve tappet 46 (thus, the stem 44 of the primary valve tappet 44) and the stem portion 60 of the intake valve 42 for reciprocatingly sliding in the cylinder head 14 of the internal combustion engine 10, as best shown in FIGS. 2 and 3. The valve guide 70 is fixed in the cylinder head 14 in any appropriate manner known in the art, such by press-fit connection.

Furthermore, the tappet head 50 of the primary valve tappet 44 has a primary tappet surface 52 facing the valve head 62 of the intake valve 42 and complementary to the first contact surface 64 of the intake valve 42. The primary tappet surface 52 of the primary valve tappet 44 is provided for engaging the complementary first contact surface 64 of the intake valve 42. Correspondingly, the tubular stem 54 of the secondary valve tappet 46 has a secondary tappet surface 58 (preferably annular in configuration) provided on axially bottom end thereof facing the intake valve 42, as shown in detail in FIG. 4, and complementary to the second contact surface 63 of the intake valve 42. The secondary tappet surface 58 of the secondary valve tappet 46 is provided for engaging the complementary secondary contact surface 63 of the intake valve 42, as shown in FIG. 3.

The secondary tappet surface 58 of the secondary valve tappet 46 is axially spaced to the distance k (best shown in FIG. 7) from the complementary second contact surface 63 of the intake valve 42 when the first contact surface 64 of the valve head 62 of the intake valve 42 is in engagement with the complementary primary tappet surface 52 of the tappet head 50 of the primary valve tappet 44 as illustrated in FIGS. 1 and 2, so as to allow the intake valve 42 to slide (or axially move) back and forth along the stem 48 of the primary valve tappet 44 in a free floating manner between the primary tappet surface 52 of the primary valve tappet 44 and the secondary tappet surface 58 of the secondary valve tappet 46 when the primary tappet surface 52 of the primary valve tappet 44 is axially spaced from the first contact surface 64 of the intake valve 42. In other words, the poppet valve 42 is axially freely movable relative to the stem 48 of the primary valve tappet 44. Preferably, the primary tappet surface 52 of the disk-shaped tappet head 50 of the primary valve tappet 44 is conical or dome-shaped and configured to complement the first contact surface 64 of the valve head 62 of the intake valve 42, as illustrated in detail in FIG. 2.

As the primary valve tappet 44 is biased in the innermost position thereof by the expansion force of the valve spring 68, consequently, the primary tappet surface 52 of the primary valve tappet 44 is biased by the valve spring 68 to engage the complementary first contact surface 64 of the intake valve 42 so as to axially move the intake valve 42 toward the closed position thereof. Therefore, the primary valve tappet 44 is continuously (or normally) biased in the innermost position thereof by the valve spring 68, while the intake valve 42 is biased in the closed positions thereof by the expansion force of the valve spring 68 only when engaged by the primary tappet surface 52 of the primary valve tappet 44.

Therefore, the intake valve 42 is operated mechanically by both the primary and secondary valve tappets 44 and 46, respectively. Specifically, the intake valve 42 is configured for operative engagement with the primary tappet surface 52 of the primary valve tappet 44 to mechanically close the intake valve 42 when the primary valve tappet 44 is moving toward the innermost position thereof, and for operative engagement with secondary tappet surface 58 of the secondary valve tappet 46 to mechanically open the intake valve 42 when the primary valve tappet 44 is moving toward the outermost position thereof.

The intake valve assembly 30 is mechanically controlled by the single intake lobe 38 a In other words, the primary valve tappet 44 is actuated by the cam lobe 38 a. However, the geometry of the cam lobe is novel to this valve assembly. The intake valve 42 and primary valve tappet 44 are arranged coaxially and linearly (i.e. stacked one on top of the other). Both the intake valve 42 and the primary valve tappet 44 have a clearance area: a valve lash (or valve clearance) of the primary valve tappet 44 defined as a distance between a distal end of the stem 48 of the primary valve tappet 44 and the rocker arm 36 a, and a valve lash (or valve clearance) of the intake valve 42 defined as the distance k (best shown in FIG. 7) between the secondary tappet surface 58 of the secondary valve tappet 46 and the complementary second contact surface 63 of the intake valve 42 in axial direction along the stem 48 of the primary valve tappet 44 when the first contact surface 64 of the valve head 62 of the intake valve 42 is in engagement with the complementary primary tappet surface 52 of the tappet head 50 of the primary valve tappet 44, or when the intake valve 42 is in the closed position thereof while the primary valve tappet 44 is in the innermost position thereof. In other words, the valve lash provides a free movement or a distance the valve train has to travel before mechanical contact is achieved.

Conventionally, valve lash is used to ensure a positive seal between the valve and its seat. Accordingly, the valve lash of the primary valve tappet 44 is conventional. The mechanical valve timing of the intake valve 42 is just before top dead center and just after bottom dead center. This requires an abnormal amount of distance (or clearance) between the secondary valve tappet 46 fixed to the stem 48 of the primary valve tappet 44 and the intake valve 42.

There are mechanical limits to which valve trains can operate valves. An opening ramp on the leading flank of the intake cam lobe starts the intake rocker arm upward rather slowly in the initial stages to take up any residual stack and reduce the shock-loading transferred to the valve train. However, once the valve is moving, it is best to accelerate it at a maximum rate. This same principle holds true in the last stages of closing of the valve. The valve train has to slow the valve down before it returns it down to its seat. In other words, the conventional cam lobe includes the leading flank and the trailing flank having a substantially constant gradient between minimum and maximum lifts.

Because the secondary valve tappet 46, which operates the intake valve 42, is fixed to the primary valve tappet 44, and the amount of distance required between the secondary valve tappet 46 and the intake valve 42, a conventional cam profile (with constant gradient) would have a velocity of the secondary valve tappet 46 too high at the time it made contact with the intake valve 42. Because of this fact, a cam profile of the intake cam lobe 38 a according to the present invention is designed to accommodate the intake valve assembly 30 of the present invention. Specifically, the cam profile of the leading flank 38′ of the intake cam lobe 38 a is such that it contacts the primary valve tappet 44 conventionally and starts moving it at a rate that will allow it to slow down and safely contact the intake valve 42. In other words, the leading flank 38′ of the intake cam lobe 38 a of the present invention has a variable gradient between minimum and maximum lifts. Preferably, the trailing flank 38″ of the intake cam lobe 38 a has a conventional profile. Alternatively, the same principal can be applied to the trailing flank 38″ of the intake cam lobe 38 a so as to slow down the primary valve tappet 44 to a safe rate to engage the intake valve 42 and to return the intake valve 42 to its seat 25. In other words, both the leading flank 38′ and the trailing flank 38″ of the intake cam lobe 38 a of the present invention may have a variable gradient between minimum and maximum lifts.

More specifically, as illustrated in FIG. 8A, the leading flank 38′ of the intake cam lobe 38 a conventionally starts upward rather slowly in the initial stages to take up any residual slack and reduce the shock-loading transferred to the valve train (segment I of the cam lift, or the opening ramp of the cam lobe profile). Once the primary valve tappet 44 is moving, the gradient of the leading flank 38′ increases (segment II of the cam lift of the cam lobe profile) so as to accelerate opening of the primary valve tappet 44. Then, the gradient of the leading flank 38′ significantly decreases (segment III of the cam lift) so as to slow down and safely contact the intake valve 42 with the secondary valve tappet 46. Subsequently, the gradient of the leading flank 38′ considerably increases again (segment IV of the cam lift) so as to accelerate both the intake valve 42 at a maximum rate toward the open position thereof. When the intake valve 42 is reaching its fully open position, the gradient of the leading flank 38′ again decreases (segment V of the cam lift).

Similarly, the gradient of the trailing flank 38″ of the intake cam lobe 38 a first gradually increases (segment VI of the cam lift). Subsequently, the gradient of the trailing flank 38″ considerably increases (segment VII of the cam lift) so as to accelerate both the primary valve tappet 44 and the intake valve 42 at a maximum rate toward their respective closed position. Then, the gradient of the trailing flank 38″ significantly decreases (segment VIII of the cam lift) so as to slow down before the intake valve 42 engages the valve seat 25. In other words, the leading flank 38′ of the intake cam lobe 38 a according to the present invention has a variable gradient between minimum and maximum lifts of the primary valve tappet 44.

The primary valve tappet 44 has a fixed duration and lift defined by a geometry (or profile) of the intake lobe 38 a of the valve actuating cam 38 suitable for high speed performance, while the intake valve 42 has a variable duration and lift when actuated fluidly (pneumatically) and fixed duration and lift when actuated mechanically suitable for both low and high engine speed performance defined by the geometry of the intake lobe 38 a of the valve actuating cam 38, by the valve clearance of the intake valve 42 (i.e. the distance k between the secondary tappet surface 58 of the secondary valve tappet 46 and the complementary second contact surface 63 of the intake valve 42 in axial direction along the stem 48 of the primary valve tappet 44 when the intake valve 42 is in the closed position thereof while the primary valve tappet 44 is in the innermost position thereof), and by a spring rate (coefficient of elasticity) of the valve spring 68. More specifically, the intake valve 42 is operated mechanically by the primary and secondary valve tappets 44 and 46, respectively, and fluidly (or pneumatically) in response to pressure differential between the intake passage 18 and the combustion chamber 15. The intake valve 42 is engagable with the secondary valve tappet 46 after moving of the primary valve tappet 44 away from the intake valve 42 so that further movement of the primary valve tappet 44 toward the outermost position thereof pushes the intake valve 42 away from the valve seat 25. Free movement of the intake valve 42 (the amount controlled pneumatically) is always restricted between and the primary tappet surface 52 of the primary valve tappet 44 and the secondary tappet surface 58 of the secondary valve tappet 46. Such an arrangement of the intake valve assembly 30 provides the fluidly actuateable intake valve 42 with the ability to operate at high engine speeds. In other words, when the primary valve tappet 44 is in its outermost position—the intake valve 42 is also opened by the secondary valve tappet 46 (as illustrated in FIG. 3), and when the primary valve tappet 44 is in its innermost position—the intake valve 42 is also closed (as illustrated in FIGS. 1 and 2).

On the other hand, the medium that regulates the variable valve timing of the intake valve 42 between the two fixed mechanical actuation positions is the pressure and flow of the gas acting directly on the intake valve 42. When gas flow and pressure in the intake passage 18 fall below the minimum to open the intake port 20 (usually at the low engine speed), the secondary valve tappet 46 will open the intake valve 42 at the fixed point. A similar control is in effect at the intake valve closing. The intake valve 42 will be returned to the valve seat 25 either against the secondary tappet surface 58 of the secondary valve tappet 46 by the pressure differential between the intake passage 18 and the combustion chamber 15, or against the primary tappet surface 52 of the primary valve tappet 44 by a return spring tension of the return valve spring 68 through the primary valve tappet 44.

The exhaust valve assembly 32 is substantially conventional and includes an exhaust poppet valve 72 normally biased toward a closed position thereof by an exhaust valve spring 74, as shown in FIG. 1. Preferably, the exhaust valve spring 74 is in the form of a compression coils spring. The exhaust poppet valve 72 has a fixed duration and lift defined by the geometry of the exhaust lobe 38 b of the valve actuating cam 38.

The operation of the intake valve 42 is hybrid in nature. In other words, the intake valve 42 is operated both mechanically by the same intake lobe 38 a of the valve actuating cam 38 as the primary valve tappet 44 using the secondary valve tappet 46 fixed to the stem 44 of the primary valve tappet 44 as its mechanical lifter, and fluidly (or pneumatically) by pressure differential between the intake passage 18 and the combustion chamber 15. Specifically, the intake valve 42 can be displaced toward its open position either mechanically, when the secondary valve tappet 46 engages the second contact surface 63 of the intake valve 42 due to the movement of the primary valve tappet 44 in the direction toward the outermost position thereof, or fluidly (pneumatically), when the pressure differential between the intake passage 18 and the combustion chamber 15 reaches a predetermined value capable to overcome the friction force and move the intake valve 42 in an opening direction thereof. More specifically, when gas pressure differential between the intake passage 18 and the combustion chamber 15 is higher than the predetermined value to open the intake valve 42 (i.e. the gas pressure in the intake passage 18 is higher than the gas pressure in the combustion chamber 15 and the friction force between the intake valve 42 and the stem 48 of the primary valve tappet 44), the intake valve 42 would be opened without mechanical intervention of the secondary valve tappet 46 (if the primary valve tappet 44 is not in its innermost position). Also, when gas pressure differential between the intake passage 18 and the combustion chamber 15 falls below the predetermined value to open the intake valve 42 (i.e. the gas pressure in the intake passage 18 is lower than the gas pressure in the combustion chamber 15 and the friction force between the intake valve 42 and the stem 48 of the primary valve tappet 44), the mechanical secondary valve tappet 46 will open the intake valve 42 at the fixed point. Similarly, when gas pressure differential between the intake passage 18 and the combustion chamber 15 falls below the predetermined value, the intake valve 42 will be returned to its seat 25 fluidly due to the gas pressure differential or mechanically by the primary tappet surface 52 of the primary valve tappet 44 due to the spring tension of the valve spring 68 as the primary valve tappet 44 moves toward its innermost position. Accordingly, the present invention provides in effect a variable valve timing. Also, only minimal low cost modification is required to adapt the intake valve assembly 30 of the present invention to existing engines.

The mechanical opening and closing points of the intake valve 42 are determined by the distance k (or valve clearance) between the secondary valve tappet 46 and the stem portion 60 of the intake valve 42 when the primary valve tappet 44 is in the innermost position thereof. The fluid operated opening and closing duration and a lift rate of the intake valve 42 are determined by the valve clearance and the pressure and flow differential of gases between the intake passage 18 and the combustion chamber 15.

FIG. 9 illustrates a valve overlap (i.e. the overlap of the ending phase of the exhaust stroke and the beginning phase of the intake stroke) at low engine speed when the piston 16 is moving up and is near its top dead center (TDC) position. A valve overlap in the art of the internal combustion engines is defined as the overlap of the ending phase of the exhaust stroke and the beginning phase of the intake stroke, because typically, the intake phase of the four stroke cycle begins before the exhaust phase ends. This is the time when both the induction and exhaust ports are open to the atmosphere. This time period when both the intake poppet valve 40 and the exhaust poppet valve 72 are simultaneously open is called a valve overlap period. This is critical to exhaust gas scavenging and maximizing cylinder charging. However the efficiency of this process is very sensitive to valve timing versus engine speed. The most desirable solution is to adjust both intake and exhaust timing at the overlap. However, timing the intake valve opening has the most influence. The ending of the induction cycle happens at intake close and is also sensitive to engine speed as it relates to charging efficiency. When the conventional intake valve of a four stroke engine is replaced with the variable timing valve assembly of the present invention, the intake opening and closing timings are automatically optimized with respect to engine speed and load.

The operation of the intake valve assembly 30 of the present invention at low speeds of the engine 10, illustrated in FIGS. 9 and 10, is as follows.

FIG. 9 illustrates engine operation during a beginning phase of an induction stroke of the engine 10 at low engine speed when the piston 16 is moving up and is near its top dead center (TDC) position. During this phase, the combustion chamber 15 is filled with exhaust gas, and the exhaust poppet valve 72 is still open to enable the exhaust gas to escape from the combustion chamber 15. As the piston 16 is reaching its top dead center (TDC) position to begin the intake stroke, the valve actuating mechanism 34 for the associated intake valve assembly 30 is operated so that the stem 48 of the primary valve tappet 44 is pushed downwardly toward the outermost position thereof by the cam lobe 38 a and the first rocker arm 36 a forcing the tappet head 50 of the primary valve tappet 44 away from the valve head 62 of the intake valve 42. Initially, as the primary valve tappet 44 moves downwardly, the intake valve 42 remains seated on the valve seat 25 as the pressure of the exhaust gas in the combustion chamber 15 is higher than the pressure of the air-fuel mixture in the intake passage 18 at the low engine speeds. In other words, the valve head 62 of the intake poppet valve 42 is pressed against the valve seat 25 by the pressure differential between the combustion chamber 15 and the intake passage 18, as shown in FIG. 9. It will be appreciated that during this phase of the intake stroke, although the tappet head 50 of the primary valve tappet 44 is spaced from the valve head 62 of the intake valve 42, the intake port 20 is blocked by the intake valve 42 so as to reduce valve overlap period and prevent fluid communication between the combustion chamber 15 and the intake passage 18, thus preventing back-flow of exhaust gas through the intake port 20 into the intake passage 18 and, consequently, dilution of the air-fuel mixture in the intake passage 18. This, in turn, increasing fuel economy and reduces exhaust emission. The secondary valve tappet 46 will mechanically open the intake valve 42 before the piston 16 begins its downward movement.

Therefore, during the reduced valve overlap period (the beginning phase of the induction stroke) at low engine speeds, the intake valve 42 is closed until the secondary valve tappet 46 engages the stem portion 60 of the intake valve 42 due to the movement of the tappet head 50 of the primary valve tappet 44 in the direction away from the valve head 62 of the intake valve 42. Further downward movement of the primary valve tappet 44 (in the direction away from the intake valve 42) opens the intake valve 42, which opens the intake port 20 and provides fluid communication between the combustion chamber 15 and the intake passage 18.

FIG. 10 illustrates an ending phase of an induction stroke (or a crossover phase from the induction stroke to the compression stroke) at low engine speed when the engine 10 has reached the end of the intake stroke and the piston 16 is just started moving up to compress the gas in the combustion chamber 15 and is near its bottom dead center (BDC) position. During this time, the combustion chamber 15 is filled with the air-fuel mixture, the exhaust valve 72 is closed, while the intake valve 42 is closing but still off the valve seat 25. As the piston 16 is rising and compressing the air-fuel mixture, the gas pressure in the cylinder 12 increases well above the gas pressure inside the intake passage 18. It should be appreciated that at the low engine speeds the speed of the gas flow, thus the pressure, in the intake passage 18 is relatively low. Therefore, the gas pressure in the intake passage 18 is not enough to overcome the gas pressure in the combustion chamber 15. The gas pressure differential between the intake passage 18 and the combustion chamber 15 presses the intake valve 42 against the valve seat 25, as shown in FIG. 10. It will be appreciated that during this phase of the intake stroke, although the tappet head 50 of the primary valve tappet 44 is spaced from the valve head 62 of the intake valve 42, the intake port 20 is blocked by the valve head 62 of the intake valve 42 so as to prevent fluid communication between the combustion chamber 15 and the intake passage 18, thus preventing reverse pulsing of the air-fuel mixture through the intake port 20 back into the intake passage 18 and, consequently, improving engine torque and power. Therefore, the intake valve assembly 30 of the present invention in effect reduces the valve open duration at low engine speeds as compared to conventional engines.

The operation of the intake valve assembly 30 of the present invention at high speeds of the engine 10, illustrated in FIGS. 11 and 12, is as follows.

FIG. 11 illustrates the valve overlap (i.e. the overlap of the ending phase of the exhaust stroke and the beginning phase of the intake stroke) and engine operation during the beginning phase of the induction stroke of the engine 10 at high engine speed when the piston 16 is moving up and is near its TDC position. During this time, the exhaust poppet valve 72 is still open to enable the exhaust gas to escape from the combustion chamber 15, but is quickly closing. The high speed of the piston 16 keeps the exhaust gas velocity high in the exhaust passage 22. This draws combustion chamber pressure below atmospheric, thus, the intake 42 valve follows the mechanical opening of the primary valve tappet 44. As the piston 16 is moving up toward its TDC position to conduct the intake stroke, the valve actuating mechanism 34 for the associated intake valve assembly 30 is operated so that the stem 48 of the primary valve tappet 44 is pushed downwardly toward the outermost position thereof by the cam lobe 38 a and the first rocker arm 36 a forcing the tappet head 50 of the primary valve tappet 44 away from the valve head 62 of the intake valve 42. As the primary valve tappet 44 moves downwardly, the intake poppet valve 42 is rapidly opening, thus increasing valve overlap period (as compared to the engine operation at low engine speeds), because at the high engine speeds the fluid pressure in the intake passage 18 is well above the pressure in the combustion chamber 15. FIG. 11 illustrates the beginning phase of the intake stroke during the high speed engine operation, when the primary valve tappet 44 is moving toward the outermost position thereof by extending through the intake valve 42, while the intake valve 42 is fluidly opening earlier than during the same valving phase at low engine speeds. In other words, when the primary valve tappet 44 is moving toward the outermost position thereof at high engine speeds, the intake valve 42 is opening simultaneously as the high pressure differential between the intake passage 18 and the combustion chamber 15 (due to the high speed of the exhaust flow) as the piston 16 reaches TDC and is reversed at a high rate of acceleration of the intake flow velocity keeps the intake valve 42 open against the primary tappet surface 52 of the tappet head 50 of the primary valve tappet 44. This improves volumetric efficiency and a high end power of the engine 10.

FIG. 12 illustrates the ending phase of the induction stroke at high engine speed. The piston 16 has just completed its downward travel at very high velocity, has just reached its BDC position, and beginning to rise on the compression stroke. For that reason, the gas pressure in the combustion chamber 15 is well below the gas pressure in the intake passage 18. During this time, the exhaust poppet valve 72 is closed, and the piston 16 is moving up toward its TDC position to perform the compression stroke. In the initial phase of the compression stroke the air-fuel mixture continues to fill the cylinder 12 against the rising piston 16. The still high pressure of the air-fuel mixture flowing through the intake passage 18 keeps the valve head 62 of the intake valve 42 open against the tappet head 50 of the primary valve tappet 44. The primary valve tappet 44 and, correspondingly, the intake valve 42, are timed to close before the air-fuel mixture flow reverses. Closing of the intake valve 42 is controlled mechanically at high speed.

Therefore, the intake valve assembly 30 of the present invention reduces the opening angle and timing of the intake valve 42 at the low engine speeds so as to improve low speed performance and fuel economy of the internal combustion engine, and increases the opening angle and timing of the intake port of the intake valve 42 at high engine speeds to improve a peak power output. Accordingly, the intake valve assembly 30 of the present invention provides in effect a variable valve timing.

Detailed dynamometer test results are shown in FIGS. 13 (for stock engine) and 14 (for test engine equipped with the intake valve assembly of the present invention). The tested stock engine is a single cylinder, four-stroke engine having an engine displacement 19.02 in³. The test engine is the same single cylinder engine having the intake valve assembly of the present invention.

Therefore, the present invention provides a novel intake valve assembly of an internal combustion engine that provides in effect variable valve timing and significantly improves both low and high speed performance of the engine, reduces emissions and improves fuel economy. Moreover, the present invention requires minimal low cost modification to adapt this invention to existing engines.

The foregoing description of the preferred embodiment of the present invention has been presented for the purpose of illustration in accordance with the provisions of the Patent Statutes. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. The embodiments disclosed hereinabove were chosen in order to best illustrate the principles of the present invention and its practical application to thereby enable those of ordinary skill in the art to best utilize the invention in various embodiments and with various modifications as suited to the particular use contemplated, as long as the principles described herein are followed. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains. Thus, changes can be made in the above-described invention without departing from the intent and scope thereof. It is also intended that the scope of the present invention be defined by the claims appended thereto. 

1. An intake valve assembly of an internal combustion engine including a combustion chamber and an intake passage fluidly communicating with said combustion chamber through an intake port, said intake valve assembly comprising: an intake valve movable into and out of engagement with a valve seat formed in said intake port between respective closed and open positions so that in said closed position of said intake valve said combustion chamber being sealed from said intake passage, said intake valve having first and second contact surfaces axially spaces from each other; a primary valve tappet reciprocating between an innermost position and an outermost position, said primary valve tappet having a primary tappet surface complementary to said first contact surface of said intake valve; and a secondary valve tappet having a secondary tappet surface complementary to said second contact surface of said intake valve, said secondary valve tappet axially non-movably attached to said primary valve tappet so that said secondary tappet surface being axially spaced from said second contact surface of said intake valve when said primary tappet surface of said primary valve tappet being in engagement with said first contact surface of said intake valve; said intake valve being coaxially mounted to said primary valve tappet and axially freely movable relative thereto between said primary tappet surface of said primary valve tappet and said secondary tappet surface of said secondary valve tappet; said primary tappet surface of said primary valve tappet configured for operatively axially engaging said first contact surface of said intake valve to limit the axial movement of said intake valve away from said valve seat and to place said intake valve in said closed position thereof when said primary valve tappet being in said innermost position thereof; said secondary tappet surface of said secondary valve tappet configured for operatively axially engaging said second contact surface of said intake valve for mechanically moving said intake valve away from said valve seat; said intake valve being operated both mechanically by both said primary and secondary valve tappets and fluidly in response to pressure differential between said intake passage and said combustion chamber.
 2. The intake valve assembly as defined in claim 1, wherein said combustion chamber fluidly communicates with said intake passage only when said intake valve is in said open position.
 3. The intake valve assembly as defined in claim 2, wherein said first contact surface of said intake valve is configured for operative engagement with said primary tappet surface of said primary valve tappet to mechanically close said intake valve and said second contact surface of said intake valve is configured for operative engagement with said secondary tappet surface of said secondary valve tappet to mechanically open said intake valve.
 4. The intake valve assembly as defined in claim 3, wherein said intake valve is axially freely movable along said primary valve tappet in response to pressure differential between said intake passage and said combustion chamber when said primary tappet surface of said primary valve tappet is axially spaced from said first contact surface of said intake valve.
 5. The intake valve assembly as defined in claim 4, further comprising a valve spring for normally biasing said primary valve tappet toward said innermost position thereof and said intake valve to said closed position thereof through said primary valve tappet.
 6. The intake valve assembly as defined in claim 5, wherein said primary valve tappet includes an elongated stem and a tappet head provided at a distal end of said stem, said tappet head of said primary valve tappet is provided with said primary tappet surface.
 7. The intake valve assembly as defined in claim 6, wherein said intake valve is a poppet valve including a stem portion, a valve head complementary to said valve seat for sealingly engaging said valve seat and a substantially cylindrical bore extending through both said stem portion and said valve head of said intake valve; and wherein a distal end of said valve head of said intake valve is provided with said first contact surface and a distal end of said stem portion of said intake valve is provided with said second contact surface.
 8. The intake valve assembly as defined in claim 7, wherein said valve head of said intake valve is shaped so that said first contact surface thereof is configured to complement said primary tappet surface of said tappet head of said primary valve tappet.
 9. The intake valve assembly as defined in claim 7, wherein said stem of said primary valve tappet is axially extending through said cylindrical bore in said intake valve substantially coaxially therewith so that said intake valve is mounted about said stem of said primary valve tappet and axially freely movable relative thereto between said primary tappet surface of said primary valve tappet and said secondary tappet surface of said secondary valve tappet.
 10. The intake valve assembly as defined in claim 9, wherein said secondary valve tappet is in the form of an elongated tubular stem mounted about said stem of said primary valve tappet substantially coaxially therewith.
 11. The intake valve assembly as defined in claim 10, wherein said secondary valve tappet is provided with a valve spring retainer formed integrally therewith.
 12. The intake valve assembly as defined in claim 11, wherein said valve spring is normally contracted for continuously biasing said primary valve tappet toward said innermost position thereof.
 13. The intake valve assembly as defined in claim 12, wherein said valve spring is in the form of a coil spring mounted about said elongated tubular stem of said secondary valve tappet.
 14. The intake valve assembly as defined in claim 13, further comprising a valve guide supporting said elongated tubular stem of said secondary valve tappet for reciprocatingly sliding said primary valve tappet between said innermost and outermost positions thereof.
 15. The intake valve assembly as defined in claim 13, wherein said valve guide slideably engages both said elongated tubular stem of said secondary valve tappet and said stem portion of said intake valve.
 16. The intake valve assembly as defined in claim 1, further comprising an intake cam lobe acting on said primary valve tappet; said intake cam lobe having a fixed cam profile including a leading flank and a trailing flank; said leading flank has a variable gradient such that said primary valve tappet slows down before said secondary contact surface of said secondary valve tappet contacts said second contact surface of said intake valve. 